This invention relates generally to semiconductor technology and more particularly to the method of forming polycrystalline silicon regions within an amorphous silicon film.
Polycrystalline silicon is formed by crystallizing amorphous silicon films. One method of crystallizing amorphous silicon films is Excimer Laser Annealing (ELA). Conventional ELA processes form polycrystalline films having a random polycrystalline structure. Random, as used here, means that no single crystal orientation is dominant and that polycrystalline structures consist of a mixture of crystallographic orientations in silicon. These crystallographic orientations in silicon are commonly denoted as  less than 111 greater than ,  less than 110 greater than , and  less than 100 greater than , along with their respective corollaries, as is well known in the art. Control of crystallographic orientation is generally desirable because the electrical characteristics of a polycrystalline silicon film depend upon the crystallographic orientation of the film. In addition, the uniformity of the electrical characteristics will improve if the majority of the film has a controllable texture.
ELA, as well as many other annealing methods, has not provided a means to control these microstructural characteristics and achieve a predictable and repeatable preferential crystal orientation and film texture within an annealed film. It would be desirable to have a method of producing a more uniform crystallographic orientation within a polycrystalline silicon film. It would also be desirable to be able to select a desired crystallographic orientation.
Accordingly, a method of forming a polycrystalline silicon film with a desired predominant crystal orientation is provided. The method of forming polycrystalline films on a substrate comprises the steps of: providing a substrate, depositing an amorphous silicon film on the substrate, annealing the substrate to produce a polycrytstalline film with the desired predominant crystal orientation, preferably a  less than 100 greater than  crystal orientation, and polishing the polycrystalline film to prepare the film for further processing.
The substrate can be any material which is compatible with the deposition of amorphous silicon and excimer laser annealing. For display applications, the substrate is preferably a transparent substrate such as quartz, glass or plastic.
To achieve a good quality film that is predominantly  less than 100 greater than  crystal orientation, the step of depositing the amorphous film should deposit to a thickness of at least approximately 100 nm.
The step of annealing preferably uses a laterally seeded excimer laser annealing process. The step of polishing can be accomplished by any means that would not significantly modify the crystal orientation of the film, including by chemical mechanical polishing. For some applications a final film thickness of less than 60 nm is desirable.
The method of the present invention, produces a prepared substrate comprising a polycrystalline film, which has a predominantly  less than 100 greater than  crystal orientation, overlying a carrier substrate. The final film is preferably less than 60 nm thick. For display applications, as discussed above, the carrier substrate is preferably a transparent material such as quartz, glass or plastic.